<Cascader style="width:400px;" Data="data" Clearable @bind-Value="Val">
</Cascader>

@code{

    string Val = "";
    //下面为了方便，直接从json文件加载数据
    static string dataFile = "Pages/data/data1.json";
    List<CascaderItem<string>> data = Cascader<string>.BuildDataFromJson(System.IO.File.ReadAllText(dataFile));
}